Recent diatom assemblage changes in subarctic Lake Saanajärvi, NW Finnish Lapland, and their paleoenvironmental implications

摘要: Diatoms were analysed from a 30-cm long sediment core obtained remote subarctic Lake Saanaarvi (69°03′N, 20°52′E) in order to trace possible changes the lake. Diatom assemblages relatively constant throughout core, except top 4–5 cm (approx 1850 A.D.) where relative frequencies of Aulacoseira italica subsp. subarctica, A. lirata var. biseriata, Cyclotella comensis and C. glomerata increased markedly. No significant trends observed weighted averaging (WA) reconstructed pH values. Several hypotheses, including (i) airborne pollution, (ii) climatic change, (iii) catchment disturbances have been put forth explain recent diatom assemblages. The change coincides with marked increase mean annual temperature that has documented area since termination Little Ice Age. Our evidence favours climate as main causative mechanism for compositional changes, although other explanations cannot be ruled out.